Educational experiences can be influenced by novel experiences, yet educators often overlook the influence novelty exerts on students. This quasi-experimental study manipulated prior knowledge before a zoo field trip for 210 urban 7th-grade students from 2 schools, 1 comprised mostly of low-socioeconomic status (SES) families and 1 comprised mostly ofmiddle-SES families. Students participated in 1 of 2 preparatory lessons, only 1 of which previewed field trip-related content, thereby increasing prior knowledge for half the students from each school. Prior knowledge significantly increased learner engagement,measured through attentiveness, from both schools, but in different types of behaviors. Students from the low-SES school demonstrated more attentiveness if their preparatory lesson previewed field trip material than if it was unrelated to the field trip. Students from the middle SES school displayed the same level of attentiveness in both conditions (and overall higher than the low-SES students). This study highlights complexities associated with prior knowledge and reveals strategies to help improve engagement levels for students visiting informal learning environments.